There has been a conventionally well-known technology that a diesel particulate filter (hereinafter referred to as “DPF”) is disposed as an exhaust emission control device in an exhaust passage of a diesel engine (hereinafter referred to simply as “engine”) so as to subject exhaust gas discharged from the engine to purification process in the DPF (see patent document 1). There has also been well-known technologies of disposing in the DPF an exhaust gas temperature sensor to detect a temperature of the exhaust gas discharged from the engine and an exhaust gas pressure sensor to detect a pressure of the exhaust gas discharged from the engine (see patent documents 1 and 5).
Further, there has been a well-known technology that an inside case is disposed in the interior of an outside case so as to have a double structure in the DPF, and the inside case houses oxidization catalyst or a soot filter, or the like (see, for example, patent document 3). There has also been well-known technologies that a case storing the oxidization catalyst and a case storing the soot filter are separatably coupled to each other with a bolted flange interposed between the cases (see, for example, patent documents 3 and 4).